Contact-less power transfer

ABSTRACT

There is disclosed a system and method for transferring power without requiring direct electrical conductive contacts. There is provided a primary unit having a power supply and a substantially laminar charging surface having at least one conductor that generates an electromagnetic field when a current flows therethrough and having an charging area defined within a perimeter of the surface, the at least one conductor being arranged such that electromagnetic field lines generated by the at least one conductor are substantially parallel to the plane of the surface or at least subtend an angle of 45° or less to the surface within the charging area; and at least one secondary device including at least one conductor that may be wound about a core. Because the electromagnetic field is spread over the charging area and is generally parallel or near-parallel thereto, coupling with flat secondary devices such as mobile telephones and the like is significantly improved in various orientations thereof.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of application Ser. No. 11/000,035,filed on Dec. 1, 2004, which is itself a Division of application Ser.No. 10/514,046, filed on Feb. 28, 2005.

The present application claims priority from UK patent applicationsnumbers 0210886.8 of 13^(th) May 2002, 0213024.3 of 7^(th) Jun. 2002,0225006.6 of 28^(th) Oct. 2002 and 0228425.5 of 6^(th) Dec. 2002, aswell as from U.S. patent application Ser. No. 10/326,571 of 20^(th) Dec.2002. The full contents of all of these prior patent applications ishereby incorporated into the present application by reference.

FIELD BACKGROUND OF THE INVENTION

This invention relates to a new apparatus and method for transferringpower in a contact-less fashion.

BACKGROUND OF THE INVENTION

Many of today's portable devices incorporate “secondary” power cellswhich can be recharged, saving the user the cost and inconvenience ofregularly having to purchase new cells. Example devices include cellulartelephones, laptop computers, the Palm 500 series of Personal DigitalAssistants, electric shavers and electric toothbrushes. In some of thesedevices, the cells are recharged via inductive coupling rather thandirect electrical connection. Examples include the Braun Oral B PlakControl power toothbrush, the Panasonic Digital Cordless Phone SolutionKX-PH15AL and the Panasonic multi-head men's shavers ES70/40 series.

Each of these devices typically has an adaptor or charger which takespower from mains electricity, a car cigarette lighter or other sourcesof power and converts it into a form suitable for charging the secondarycells. There are a number of problems associated with conventional meansof powering or charging these devices:

Both the characteristics of the cells within each device and the meansof connecting to them vary considerably from manufacturer tomanufacturer, and from device to device. Therefore users who own severalsuch devices must also own several different adaptors. If users aregoing away on travel, they will have to bring their collection ofchargers if they expect to use their devices during this time.

These adaptors and chargers often require users to plug a smallconnector into the device or to place the device with accurate alignmentinto a stand causing inconvenience. If users fail to plug or place theirdevice into a charger and it runs out of power, the device becomesuseless and important data stored locally in the device might even belost.

In addition, most adaptors and chargers have to be plugged into mainssockets and hence if several are used together, they take up space inplug strips and create a messy and confusing tangle of wires.

Besides the above problems with conventional methods of rechargingdevices, there are also practical problems associated with deviceshaving an open electrical contact. For example, devices cannot be usedin wet environments due to the possibility of corroding or shorting outthe contacts and also they cannot be used in flammable gaseousenvironments due to the possibility of creating electrical sparks.

Chargers which use inductive charging remove the need to have openelectrical contacts hence allowing the adaptor and device to be sealedand used in wet environments (for example the electric toothbrush asmentioned above is designed to be used in a bathroom). However suchchargers still suffer from all other problems as described above. Forexample, the devices still need to be placed accurately into a chargersuch that the device and the charger are in a predefined relativeposition (See FIGS. 1 a and 1 b). The adaptors are still only designedspecifically for a certain make and model of device and are still onlycapable of charging one device at a time. As a result, users still needto possess and manage a collection of different adaptors.

Universal chargers (such as the Maha MH-C777 Plus Universal charger)also exist such that battery packs of different shapes andcharacteristics can be removed from the device and charged using asingle device. Whilst these universal chargers eliminate the need forhaving different chargers for different devices, they create even moreinconvenience for the user in the sense that the battery packs firstneed to be removed, then the charger needs to be adjusted and thebattery pack needs to be accurately positioned in or relative to thecharger. In addition, time must be spent to determine the correct pairof battery pack metal contacts which the charger must use.

It is known from U.S. Pat. No. 3,938,018 “Induction charging system” toprovide a means for non-contact battery charging whereby an inductivecoil on the primary side aligns with a horizontal inductive coil on asecondary device when the device is placed into a cavity on the primaryside. The cavity ensures the relatively precise alignment which isnecessary with this design to ensure that good coupling is achievedbetween the primary and secondary coils.

It is also known from U.S. Pat. No. 5,959,433 “Universal InductiveBattery Charger System” to provide a non-contact battery chargingsystem. The battery charger described includes a single charging coilwhich creates magnetic flux lines which will induce an electricalcurrent in a battery pack which may belong to cellular phones or laptopcomputers.

It is also known from U.S. Pat. No. 4,873,677 “Charging Apparatus for anElectronic Device” to provide an apparatus for charging an electronicdevice which includes a pair of coils. This pair of coils is designed tooperate in anti-phase such that magnetic flux lines are coupled from onecoil to the other. An electronic device such as a watch can be placed onthese two coils to receive power.

It is also known from U.S. Pat. No. 5,952,814 “Induction chargingapparatus and an electronic device” to provide an induction charger forcharging a rechargeable battery. The shape of the external casing of theelectronic device matches the internal shape of the charger thusallowing for accurate alignment of the primary and secondary coils.

It is also known from U.S. Pat. No. 6,208,115 “Battery substitute pack”to provide a substitute battery pack which may be inductively recharged.

It is known from WO 00/61400 “Device for Inductively TransmittingElectrical Power” to provide a means of transferring power inductivelyto conveyors.

It is known from WO 95/11545 “Inductive power pick-up coils” to providea system for inductive powering of electric vehicles from a series ofin-road flat primaries.

To overcome the limitations of inductive power transfer systems whichrequire that secondary devices be axially aligned with the primary unit,one might propose that an obvious solution is to use a simple inductivepower transfer system whereby the primary unit is capable of emitting anelectromagnetic field over a large area (See FIG. 2 a). Users can simplyplace one or more devices to be recharged within range of the primaryunit, with no requirement to place them accurately. For example thisprimary unit may consist of a coil encircling a large area. When acurrent flows through the coil, an electromagnetic field extending overa large area is created and devices can be placed anywhere within thisarea. Although theoretically feasible, this method suffers from a numberof drawbacks. Firstly, the intensity of electromagnetic emissions isgoverned by regulatory limits. This means that this method can onlysupport power transfer at a limited rate. In addition, there are manyobjects that can be affected by the presence of an intense magneticfield. For example, data stored on credit cards maybe destroyed andobjects made of metal will have induced therein eddy currents generatingundesired heating effects. In addition, if a secondary device comprisinga conventional coil (see FIG. 2 a) is placed against a metallic platesuch as a copper plane in a printed circuit board or metallic can of acell, coupling is likely to be significantly reduced.

To avoid the generation of large magnetic fields, one might suggestusing an array of coils (See FIG. 3) whereby only the coils needed areactivated. This method is described in a paper published in the Journalof the Magnetics Society of Japan titled “Coil Shape in a Desk-typeContactless Power Station System” (29 Nov. 2001). In an embodiment ofthe multiple-coil concept, a sensing mechanism senses the relativelocation of the secondary device relative to the primary unit. A controlsystem then activates the appropriate coils to deliver power to thesecondary device in a localised fashion. Although this method provides asolution to the problems previously listed, it does so in a complicatedand costly way. The degree to which the primary field can be localisedis limited by the number of coils and hence the number of drivingcircuits used (i.e. the “resolution” of the primary unit). The costassociated with a multiple-coil system would severely limit thecommercial applications of this concept. Non-uniform field distributionis also a drawback. When all the coils are activated in the primaryunit, they sum to an equivalent of a large coil, the magnetic fielddistribution of which is seen to exhibit a minimum at the centre of thecoil.

Another scheme is outlined in U.S. Pat. No. 5,519,262 “Near Field PowerCoupling System”, whereby a primary unit has a number of narrowinductive coils (or alternatively capacitive plates) arranged from oneend to the other of a flat plate, creating a number of vertical fieldswhich are driven in a phase-shifted manner so that a sinusoidal wave ofactivity moves across the plate. A receiving device has two verticalfield pickups arranged so that regardless of its position on the plateit can always collect power from at least one pickup. While this schemealso offers freedom of movement of the device, it has the disadvantagesof needing a complex secondary device, having a fixed resolution, andhaving poor coupling because the return flux path is through air.

None of the prior art solutions can satisfactorily address all of theproblems that have been described. It would be convenient to have asolution which is capable of transferring power to portable devices withall of the following features and is cost effective to implement:

Universality: a single primary unit which can supply power to differentsecondary devices with different power requirements thereby eliminatingthe need for a collection of different adaptors and chargers;

Convenience: a single primary unit which allows secondary devices to beplaced anywhere within an active vicinity thereby eliminating the needfor plugging-in or placing secondary devices accurately relative to anadaptor or charger;

Multiple-load: a single primary unit that can supply power to a numberof secondary different devices with different power requirements at thesame time;

Flexibility for use in different environments: a single primary unitthat can supply power to secondary devices such that no directelectrical contact is required thereby allowing for secondary devicesand the primary unit itself to be used in wet, gaseous, clean and otheratypical environments;

Low electromagnetic emissions: a primary unit that can deliver power ina manner that will minimize the intensity and size of the magnetic fieldgenerated.

It is further to be appreciated that portable appliances areproliferating and they all need batteries to power them. Primary cells,or batteries of them, must be disposed of once used, which is expensiveand environmentally unfriendly. Secondary cells or batteries can berecharged and used again and again.

Many portable devices have receptacles for cells of an industry-standardsize and voltage, such as AA, AAA, C, D and PP3. This leaves the userfree to choose whether to use primary or secondary cells, and of varioustypes. Once depleted, secondary cells must typically be removed from thedevice and placed into a separate recharging unit. Alternatively, someportable devices do have recharging circuitry built-in, allowing cellsto be recharged in-situ once the device is plugged-in to an externalsource of power.

It is inconvenient for the user to have to either remove cells from thedevice for recharging, or to have to plug the device into an externalpower source for recharging in-situ. It would be far preferable to beable to recharge the cells without doing either, by some non-contactmeans.

Some portable devices are capable of receiving power coupled inductivelyfrom a recharger, for example the Braun Oral B Plak Control toothbrush.Such portable devices typically have a custom, dedicated power-receivingmodule built-in to the device, which then interfaces with an internalstandard cell or battery (which may or may not be removable).

However it would be convenient if the user could transform any portabledevice which accepts industry-standard cell sizes into aninductively-rechargeable device, simply by fittinginductively-rechargeable cells or batteries, which could then berecharged in-situ by placing the device onto an inductive recharger.

Examples of prior art include U.S. Pat. No. 6,208,115, which discloses asubstitute battery pack which may be inductively recharged.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention, there is provideda system for transferring power without requiring direct electricalconductive contacts, the system comprising:

i) a primary unit including a substantially laminar charging surface andat least one means for generating an electromagnetic field, the meansbeing distributed in two dimensions across a predetermined area in orparallel to the charging surface so as to define at least one chargingarea of the charging surface that is substantially coextensive with thepredetermined area, the charging area having a width and a length on thecharging surface, wherein the means is configured such that, when apredetermined current is supplied thereto and the primary unit iseffectively in electromagnetic isolation, an electromagnetic fieldgenerated by the means has electromagnetic field lines that, whenaveraged over any quarter length part of the charging area measuredparallel to a direction of the field lines, subtend an angle of 45° orless to the charging surface in proximity thereto and are distributed intwo dimensions thereover, and wherein the means has a height measuredsubstantially perpendicular to the charging area that is less thaneither of the width or the length of the charging area; and

ii) at least one secondary device including at least one electricalconductor;

wherein, when the at least one secondary device is placed on or inproximity to a charging area of the primary unit, the electromagneticfield lines couple with the at least one conductor of the at least onesecondary device and induce a current to flow therein.

According to a second aspect of the present invention, there is provideda primary unit for transferring power without requiring directelectrical conductive contacts, the primary unit including asubstantially laminar charging surface and at least one means forgenerating an electromagnetic field, the means being distributed in twodimensions across a predetermined area in or parallel to the chargingsurface so as to define at least one charging area of the chargingsurface that is substantially coextensive with the predetermined area,the charging area having a width and a length on the charging surface,wherein the means is configured such that, when a predetermined currentis supplied thereto and the primary unit is effectively inelectromagnetic isolation, an electromagnetic field generated by themeans has electromagnetic field lines that, when averaged over anyquarter length part of the charging area measured parallel to adirection of the field lines, subtend an angle of 45° or less to thecharging surface in proximity thereto and are distributed in twodimensions thereover, and wherein the means has a height measuredsubstantially perpendicular to the charging area that is less thaneither of the width or the length of the charging area.

According to a third aspect of the present invention, there is provideda method of transferring power in a non-conductive manner from a primaryunit to a secondary device, the primary unit including a substantiallylaminar charging surface and at least one means for generating anelectromagnetic field, the means being distributed in two dimensionsacross a predetermined area in or parallel to the charging surface so asto define at least one charging area of the charging surface that issubstantially coextensive with the predetermined area, the charging areahaving a width and a length on the charging surface, the means having aheight measured substantially perpendicular to the charging area that isless than either of the width or the length of the charging area, andthe secondary device having at least one electrical conductor; wherein:

i) an electromagnetic field, generated by the means when energised witha predetermined current and measured when the primary unit iseffectively in electromagnetic isolation, has electromagnetic fieldlines that, when averaged over any quarter length part of the chargingarea measured parallel to a direction of the field lines, subtend anangle of 45° or less to the charging surface in proximity thereto andare distributed in two dimensions over the at least one charging areawhen averaged thereover; and

ii) the electromagnetic field links with the conductor of the secondarydevice when this is placed on or in proximity to the charging area.

According to a fourth aspect of the present invention, there is provideda secondary device for use with the system, unit or method of the first,second or third aspects, the secondary device including at least oneelectrical conductor and having a substantially laminar form factor.

In the context of the present application, the word “laminar” defines ageometry in the form of a thin sheet or lamina. The thin sheet or laminamay be substantially flat, or may be curved.

The primary unit may include an integral power supply for the at leastone means for generating an electromagnetic field, or may be providedwith connectors or the like enabling the at least one means to beconnected to an external power supply.

In some embodiments, the means for generating the electromagnetic fieldhave a height that is no more than half the width or half the length ofthe charging area; in some embodiments, the height may be no more than ⅕of the width or ⅕ of the length of the charging area.

The at least one electrical conductor in the secondary device may bewound about a core that serves to concentrate flux therein. Inparticular, the core (where provided) may offer a path of leastresistance to flux lines of the electromagnetic field generated by theprimary unit. The core may be amorphous magnetically permeable material.In some embodiments, there is no need for an amorphous core.

Where an amorphous core is provided, it is preferred that the amorphousmagnetic material is a non-annealed or substantially as-cast state. Thematerial may be at least 70% non-annealed, or preferably at least 90%non-annealed. This is because annealing tends to make amorphous magneticmaterials brittle, which is disadvantageous when contained in a device,such as a mobile phone, which may be subjected to rough treatment, forexample by being accidentally dropped. In a particularly preferredembodiment, the amorphous magnetic material is provided in the form of aflexible ribbon, which may comprise one or more layers of one or more ofthe same or different amorphous magnetic materials. Suitable materialsinclude alloys which may contain iron, boron and silicon or othersuitable materials. The alloy is melted and then cooled so rapidly(“quenched”) that there is no time for it to crystallise as itsolidifies, thus leaving the alloy in a glass-like amorphous state.Suitable materials include Metglas® 2714A and like materials. Permalloyor mumetal or the like may also be used.

The core in the secondary device, where provided, is preferably a highmagnetic permeability core. The relative permeability of this core ispreferably at least 100, even more preferably at least 500, and mostpreferably at least 1000, with magnitudes of at least 10,000 or 100,000being particularly advantageous.

The at least one means for generating an electromagnetic field may be acoil, for example in the form of a length of wire or a printed strip, ormay be in the form of a conductive plate of appropriate configuration,or may comprise any appropriate arrangement of conductors. A preferredmaterial is copper, although other conductive materials, generallymetals, may be used as appropriate. It is to be understood that the term“coil” is here intended to encompass any appropriate electricalconductor forming an electrical circuit through which current may flowand thus generate an electromagnetic field. In particular, the “coil”need not be wound about a core or former or the like, but may be asimple or complex loop or equivalent structure.

Preferably, the charging area of the primary unit is large enough toaccommodate the conductor and/or core of the secondary device in aplurality of orientations thereof. In a particularly preferredembodiment, the charging area is large enough to accommodate theconductor and/or core of the secondary device in any orientationthereof. In this way, power transfer from the primary unit to thesecondary device may be achieved without having to align the conductorand/or core of the secondary device in any particular direction whenplacing the secondary device on the charging surface of the primaryunit.

The substantially laminar charging surface of the primary unit may besubstantially planar, or may be curved or otherwise configured to fitinto a predetermined space, such as a glove compartment of a cardashboard or the like. It is particularly preferred that the means forgenerating an electromagnetic field does not project or protrude aboveor beyond the charging surface.

A key feature of the means for generating an electromagnetic field inthe primary unit is that electromagnetic field lines generated by themeans, measured when the primary unit is effectively in magneticisolation (i.e. when no secondary device is present on or in proximityto the charging surface), are distributed in two dimensions over the atleast one charging area and subtend an angle of 45° or less to thecharging area in proximity thereto (for example, less than the height orwidth of the charging area) and over any quarter length part of thecharging area measured in a direction generally parallel to that of thefield lines. The measurement of the field lines in this connection is tobe understood as a measurement of the field lines when averaged over thequarter length of the charging area, rather than an instantaneous pointmeasurement. In some embodiments, the field lines subtend an angle of30° or less, and in some embodiments are substantially parallel to atleast a central part of the charging area in question. This is in starkcontrast to prior art systems, where the field lines tend to besubstantially perpendicular to a surface of a primary unit. Bygenerating electromagnetic fields that are more or less parallel to orat least have a significant resolved component parallel to the chargingarea, it is possible to control the field so as to cause angularvariations thereof, in or parallel to the plane of the charging area,that help to avoid any stationary nulls in the electromagnetic fieldthat would otherwise reduce charging efficiency in particularorientations of the secondary device on the charging surface. Thedirection of the field lines may be rotated through a complete orpartial circle, in one or both directions. Alternatively, the directionmay be caused to “wobble” or fluctuate, or may be switched between twoor more directions. In more complex configurations, the direction of thefield lines may vary as a Lissajous pattern or the like.

In some embodiments, the field lines may be substantially parallel toeach other over any given charging area, or at least have resolvedcomponents in or parallel to the plane of the charging area that aresubstantially parallel to each other at any given moment in time.

It is to be appreciated that one means for generating an electromagneticfield may serve to provide a field for more than one charging area; alsothat more than one means may serve to provide a field for just onecharging area. In other words, there need not be a one-to-onecorrespondence of means for generating electromagnetic fields andcharging areas.

The secondary device may adopt a substantially flat form factor with acore thickness of 2 mm or less. Using a material such as one or moreamorphous metal sheets, it is possible to have core thickness down to 1mm or less for applications where size and weight is important. See FIG.7 a.

In a preferred embodiment, the primary unit may include a pair ofconductors having adjacent coplanar windings which have mutuallysubstantially parallel linear sections arranged so as to produce asubstantially uniform electromagnetic field extending generally parallelto or subtending an angle of 45° or less to the plane of the windingsbut substantially at right angles to the parallel sections.

The windings in this embodiment may be formed in a generally spiralshape, comprising a series of turns having substantially parallelstraight sections.

Advantageously, the primary unit may include first and second pairs ofconductors which are superimposed in substantially parallel planes withthe substantially parallel linear sections of the first pair arrangedgenerally at right angles to the substantially parallel linear sectionsof the second pair, and further comprising a driving circuit which isarranged to drive them in such a way as to generate a resultant fieldwhich rotates in a plane substantially parallel to the planes of thewindings.

According to a fifth aspect of the present invention, there is provideda system for transferring power in a contact-less manner consisting of:

a primary unit consisting of at least one electrical coil whereby eachcoil features at least one active area whereby two or more conductorsare substantially distributed over this area in such a fashion that itis possible for a secondary device to be placed in proximity to a partof this active area where the net instantaneous current flow in aparticular direction is substantially non-zero;

at least one secondary device consisting of conductors wound around ahigh permeability core in such a fashion that it is possible for it tobe placed in proximity to an area of the surface of the primary unitwhere the net instantaneous current flow is substantially non-zero;

whereby the at least one secondary device is capable of receiving powerby means of electromagnetic induction when the central axis of thewinding is in proximity to the active area of the primary unit, issubstantially not perpendicular to the plane of the active area ofprimary unit and is substantially not parallel to the conductors in theactive area of at least one of the coils of the primary unit.

Where the secondary device comprises an inductively rechargeable batteryor cell, the battery or cell may have a primary axis and be capable ofbeing recharged by an alternating field flowing in the primary axis ofthe battery or cell, the battery or cell consisting of:

an enclosure and external electrical connections similar in dimensionsto industry-standard batteries or cells

an energy-storage means

an optional flux-concentrating means

a power-receiving means

a means of converting the received power to a form suitable for deliveryto outside the cell through the external electrical connections, or torecharge the energy storage means, or both.

The proposed invention is a significant departure from the design ofconventional inductive power transfer systems. The difference betweenconventional systems and the proposed system is best illustrated bylooking at their respective magnetic flux line patterns. (See FIGS. 2 aand 4)

Conventional System: In a conventional system (See FIG. 2 a), there istypically a planar primary coil which generates a magnetic field withflux lines coming out of the plane in a perpendicular fashion. Thesecondary device has typically a round or square coil that encirclessome or all of these flux lines.

Proposed system: In the proposed system, the magnetic field travelssubstantially horizontally across the surface of the plane (see FIG. 4)instead of directly out of the plane as illustrated in FIG. 2 a. Thesecondary device hence may have an elongated winding wound around amagnetic core. See FIGS. 7 a and 7 b. When the secondary device isplaced on the primary unit, the flux lines would be attracted to travelthrough the magnetic core of the secondary device because it is thelowest reluctance path. This causes the secondary device and the primaryunit to be coupled effectively. The secondary core and winding may besubstantially flattened to form a very thin component.

In describing the invention, specific terminology will be resorted tofor the sake of clarity. However, it is not intended that the inventionbe limited to the specific terms so selected and it is to be understoodthat each specific term includes all technical equivalents which operatein a similar manner to accomplish a similar purpose.

It is to be understood that the term “charging area” used in this patentapplication may refer to the area of the at least one means forgenerating a field (e.g. one or more conductors in the form of a coil)or an area formed by a combination of primary conductors where thesecondary device can couple flux effectively. Some embodiments of thisare shown in FIGS. 6 a to 61 and 9 c as component 740. A feature of a“charging area” is a distribution of conductors over a significant areaof the primary unit configured such that it is possible for the at leastone means for generating a field to be driven to achieve aninstantaneous net flow of flux in one direction. A primary unit may havemore than one charging area. One charging area is distinct from anothercharging area when flux cannot be effectively coupled by the secondarydevice (such as those shown in FIG. 7 a) in any rotation at theboundary.

It is to be understood that the term “coil” used in this patent refersto all conductor configurations which feature a charging area asdescribed above. This includes windings of wire or printed tracks or aplane as shown in FIG. 8 e. The conductors may be made of copper, gold,alloys or any other appropriate material.

The present application refers to the rotation of a secondary device inseveral places. It is to be clarified here that if a secondary device isrotated, the axis of rotation being referred to is the one perpendicularto the plane of the charging area.

This radical change in design overcomes a number of drawbacks ofconventional systems. The benefits of the proposed invention include:

No need for accurate alignment: The secondary device can be placedanywhere on a charging area of the primary unit;

Uniform coupling: In the proposed invention, the coupling between theprimary unit and secondary device is much more uniform over the chargingarea compared to a conventional primary and secondary coil. In aconventional large coil system (see FIG. 2 a), the field strength dipsto a minimum at the centre of the coil, in the plane of the coil (seeFIG. 2 b). This implies that if sufficient power is to be effectivelytransferred at the centre, the field strength at the minimum has to beabove a certain threshold. The field strength at the maximum will thenbe excessively higher than the required threshold and this may causeundesirable effects.

Universality: a number of different secondary devices, even those havingdifferent power requirements, can be placed within charging areas on thecharging surface of the primary unit to receive power simultaneously;

Increased coupling coefficiency: Optional high permeability magneticmaterial present in the secondary device increases the induced fluxsignificantly by offering a low reluctance path. This can significantlyincrease the power transfer.

Desirable form factor for secondary device: The geometry of the systemallows thin sheets of magnetic material (such as amorphous metalribbons) to be used. This means that secondary devices can have the formfactor of a thin sheet, making it suitable to be incorporated at theback of mobile phones and other electronic devices. If magnetic materialwas to be used in the centre of conventional coils, it is likely toincrease the bulkiness of the secondary device.

Minimised field leakage: When one or more secondary devices are presentin the charging area of the primary unit, it is possible to use magneticmaterial in such a way that more than half of the magnetic circuit islow reluctance magnetic material (see FIG. 4 d). This means that moreflux flows for a given magneto-motive force (mmf). As the inducedvoltage is proportional to the rate of change of flux linked, this willincrease the power transfer to the secondary device. The fewer andshorter the air gaps are in the magnetic circuit, the less the fieldwill fringe, the closer the flux is kept to the surface of the primaryunit and hence leakage is minimized.

Cost effectiveness: Unlike the multiple-coil design, this solutionrequires a much simpler control system and fewer components.

Free axial rotation of secondary device: If the secondary device is thinor optionally even cylindrical (see FIG. 10), it may be constructed suchthat it continues to couple well to the flux regardless of its rotationabout its longest axis. This may in particular be an advantage if thesecondary device is a battery cell fitted within another device, whenits axial rotation may be difficult to control.

The magnetic core in the secondary device may be located near otherparallel planes of metal within or near the device, for example a copperprinted circuit board or aluminium cover. In this case, the performanceof embodiments of the present invention is significantly better thanthat of a conventional core-wound coil because the field lines through aconventional device coil will suffer flux-exclusion if the coil isplaced up against the metal plane (because the lines of flux must travelperpendicular to the plane of the coil). Since in embodiments of thepresent invention the lines of flux travel along the plane of the core,and therefore also of the metal plane, performance is improved. Anadditional benefit is that the magnetic core in a secondary device ofembodiments of the present invention can act as a shield between theelectromagnetic field generated by the primary unit and any items (e.g.electrical circuits, battery cells) on the other side of the magneticcore.

Because its permeability is higher than that of air, the magnetic coreof the secondary device of embodiments of the present invention acts toconcentrate magnetic flux, thus capturing more flux than would otherwiseflow through an equivalent cross-section of air. The size of the core's“shape factor” (the equivalent flux-capturing sphere) is determined to afirst-order approximation by the longest planar dimension of the core.Therefore if the core of the secondary device of embodiments of thepresent invention has planar dimensions with a significantly non-squareaspect ratio, for example a 4:1 rectangle instead of a 1:1 square, itwill capture proportionally more of any flux travelling parallel to thedirection of its longest planar dimension. Therefore if used in deviceswhich have a constrained aspect ratio (for example a long thin devicesuch as a headset or pen), a significant increase in performance will beexperienced compared with that of a conventional coil of the same area.

The primary unit typically consists of the following components. (SeeFIG. 5)

Power supply: This power supply converts mains voltage into a lowervoltage dc supply. This is typically a conventional transformer or aswitch-mode power supply;

Control unit: The control unit serves the function of maintaining theresonance of the circuit given that the inductance of the means forgenerating a field changes with the presence of secondary devices. Toenable this function, the control unit may be coupled to a sensing unitwhich feeds back the current status of the circuit. It may also becoupled to a library of capacitors which may be switched in and out asrequired. If the means for generating a field requires more than onedriving circuit, the control unit may also coordinate the parameterssuch as the phase difference or on/off times of different drivingcircuits such that the desired effect is achieved. It is also possiblefor the Q (quality factor) of the system to be designed to function overa range of inductances such that a need for the above control system iseliminated;

Driving circuit: The driving unit is controlled by the control unit anddrives a changing current through the means for generating a field or acomponent of the means. More than one driving circuit may be presentdepending on the number of independent components in the means;

Means for generating an electromagnetic field: The means uses currentsupplied from the driving circuits to generate electromagnetic fields ofpre-defined shapes and intensities. The exact configuration of the meansdefines the shape and intensity of the field generated. The means mayinclude magnetic material to act as flux guides and also one or moreindependently driven components (windings), together forming thecharging area. A number of embodiment designs are possible and examplesare shown in FIGS. 6.

Sensing unit: The sensing unit retrieves and sends relevant data to thecontrol unit for interpretation.

The secondary device typically consists of the following components, asshown in FIG. 5.

Magnetic unit: the magnetic unit converts the energy stored in themagnetic field generated by the primary unit back into electricalenergy. This is typically implemented by means of a winding wound arounda highly permeable magnetic core. The largest dimension of the coretypically coincides with the central axis of the winding.

Conversion unit: the conversion unit converts the fluctuating currentreceived from the magnetic unit into a form that is useful to the devicethat it is coupled to. For example, the conversion unit may convert thefluctuating current into an unregulated dc supply by means of afull-wave bridge rectifier and smoothing capacitor. In other cases, theconversion unit may be coupled to a heating element or a batterycharger. There is also typically a capacitor present either in parallelor in series with the magnetic unit to form a resonant circuit at theoperating frequency of the primary unit.

In typical operation, one or more secondary devices are placed on top ofthe charging surface of the primary unit. The flux flows through the atleast one conductor and/or core of the secondary devices present andcurrent is induced. Depending on the configuration of the means forgenerating a field in the primary unit, the rotational orientation ofthe secondary device may affect the amount of flux coupled.

The Primary Unit

The primary unit may exist in many different forms, for example:

As a flat platform or pad which can sit on top of tables and other flatsurfaces;

Built in to furniture such as desks, tables, counters, chairs, bookcasesetc. such that the primary unit may not be visible;

As part of an enclosure such as a drawer, a box, a glove compartment ofa car, a container for power tools;

As a flat platform or pad which can be attached to a wall and usedvertically.

The primary unit may be powered from different sources, for example:

A mains AC power outlet

A vehicle lighter socket

Batteries

Fuel Cells

Solar Panel

Human power

The primary unit may be small enough such that only one secondary devicemay be accommodated on the charging surface in a single charging area,or may be large enough to accommodate many secondary devicessimultaneously, sometimes in different charging areas.

The means for generating a field in the primary unit may be driven atmains frequency (50 Hz or 60 Hz) or at some higher frequency.

The sensing unit of the primary unit may sense the presence of secondarydevices, the number of secondary devices present and even the presenceof other magnetic material which is not part of a secondary device. Thisinformation may be used to control the current being delivered to thefield generating means of the primary unit.

The primary unit and/or the secondary device may be substantiallywaterproof or explosion proof.

The primary unit and/or the secondary device may be hermetically sealedto standards such as IP66.

The primary unit may incorporate visual indicators (for example, but notlimited to, light emitting devices, such as light emitting diodes,electrophosphorescent displays, light emitting polymers, or lightreflecting devices, such as liquid crystal displays or MITs electronicpaper) to indicate the current state of the primary unit, the presenceof secondary devices or the number of secondary devices present or anycombination of the above.

The Means For Generating An Electromagnetic Field

The field generating means as referred to in this application includesall configurations of conductors where:

The conductors are substantially distributed in the plane and;

Substantial areas of the plane exist where there is a non-zero netinstantaneous current flow. These are areas on which, given the correctorientation, the secondary devices will couple effectively and receivepower. (See FIG. 6)

The conductors are capable of generating an electromagnetic field wherethe field lines subtend an angle of 45° or less or are substantiallyparallel to a substantial area of the plane.

FIGS. 6 illustrate some possibilities for such a primary conductor.Although most of the configurations are in fact coil windings, it is tobe appreciated that the same effect can also be achieved with conductorplanes which are not typically considered to be coils (See FIG. 6 e).These drawings are typical examples and are non-exhaustive. Theseconductors or coils may be used in combination such that the secondarydevice can couple effectively in all rotations whilst on the chargingarea(s) of the primary unit.

Magnetic Material

It is possible to use magnetic materials in the primary unit to enhanceperformance.

Magnetic material may be placed below one or more charging areas or theentire charging surface such that there is also a low reluctance path onthe underside of the conductors for the flux to complete its path.According to theory, an analogy can be drawn between magnetic circuitsand electrical circuits. Voltage is analogous to magneto-motive force(mmf), resistance is analogous to reluctance and current is analogous toflux. From this, it can be seen that for a given mmf, flux flow willincrease if the reluctance of the path is decreased. By providingmagnetic material to the underside of the charging area, the reluctanceof the magnetic circuit is essentially decreased. This substantiallyincreases the flux linked by the secondary device and ultimatelyincreases the power transferred. FIG. 4 d illustrates a sheet ofmagnetic material placed underneath the charging area and the resultingmagnetic circuit.

Magnetic material may also be placed above the charging surface and/orcharging area(s) and below the secondary devices to act as a flux guide.This flux guide performs two functions: Firstly, the reluctance of thewhole magnetic circuit is further decreased allowing more flux to flow.Secondly, it provides a low reluctance path along the top surface of thecharging area(s) so the flux lines will flow through these flux guidesin favour of flowing through the air. Hence this has the effect ofcontaining the field close to the charging surface of the primary unitinstead of in the air. The magnetic material used for flux guides may bestrategically or deliberately chosen to have different magneticproperties to the magnetic core (where provided) of the secondarydevice. For example, a material with lower permeability and highersaturation may be chosen. High saturation means that the material cancarry more flux and the lower permeability means that when a secondarydevice is in proximity, a significant amount of flux would then chooseto travel through the secondary device in favour of the flux guide. (SeeFIGS. 8)

In some configurations of the primary unit field generating means, theremay be conductors present that do not form part of the charging area,such as the component marked 745 in FIGS. 6 a and 6 b. In such cases,one may wish to use magnetic material to shield the effects of theseconductors.

Examples of some materials which may be used include but are not limitedto: amorphous metal (metallic glass alloys such as MetGlas™), mesh ofwires made of magnetic material, steel, ferrite cores, mumetal andpermalloy.

The Secondary Device

The secondary device may take a variety of shapes and forms. Generally,in order for good flux linkage, a central axis of the conductor (forexample, a coil winding) should be substantially non-perpendicular tothe charging area(s).

The secondary device may be in the shape of a flattened winding. (SeeFIG. 7 a) The magnetic core inside can consist of sheets of magneticmaterial such as amorphous metals. This geometry allows the secondarydevice to be incorporated at the back of electronic devices such asmobile phones, personal digital assistants and laptops without addingbulk to the device.

The secondary device may be in the shape of a long cylinder. A longcylindrical core could be wound with conductors (See FIG. 7 b).

The secondary device may be an object with magnetic material wrappedaround it. An example is a standard-sized (AA, AAA, C, D) or othersized/shaped (e.g. dedicated/customised for particular applications)rechargeable battery cell with for example magnetic material wrappedaround the cylinder and windings around the cylindrical body.

The secondary device may be a combination of two or more of the above.The above embodiments may even be combined with a conventional coil.

The following non-exhaustive list illustrates some examples of objectsthat can be coupled to a secondary device to receive power.Possibilities are not limited to those described below:

A mobile communication device, for example a radio, mobile telephone orwalkie-talkie;

A portable computing device, for example a personal digital assistant orpalmtop or laptop computer;

Portable entertainment devices, for example a music player, gamesconsole or toy;

Personal care items, for example a toothbrush, shaver, hair curler, hairrollers;

A portable imaging device, for example a video camcorder or a camera;

Containers of contents that may require heating, for example coffeemugs, plates, cooking pots, nail-polish and cosmetic containers;

Consumer devices, for example torches, clocks and fans;

Power tools, for example cordless drills and screwdrivers;

Wireless peripheral devices, for example wireless computer mouse,keyboard and headset;

Time keeping devices, for example clock, wrist watch, stop watch andalarm clock;

A battery-pack for insertion into any of the above;

A standard-sized battery cell.

In the case of unintelligent secondary devices such as a battery cell,some sophisticated charge-control means may also be necessary to meterinductive power to the cell and to deal with situations where multiplecells in a device have different charge states. Furthermore, it becomesmore important for the primary unit to be able to indicate a “charged”condition, since the secondary cell or battery may not be easily visiblewhen located inside another electrical device.

A possible system comprising an inductively rechargeable battery or celland a primary unit is shown in FIG. 10. In addition to the freedom toplace the battery 920 freely in (X,Y) and optionally rotate it in rZ,relative to the primary unit 910, the battery can also be rotated alongits axis rA while continuing to receive power.

When a user inserts a battery into a portable device, it is not easy toensure that it has any given axial rotation. Therefore, embodiments ofthe present invention are highly advantageous because they can ensurethat the battery can receive power while in any random orientation aboutrA.

The battery or cell may include a flux concentrating means that may bearranged in a variety of ways:

1. As shown in FIG. 11 a, a cell 930 may be wrapped in a cylinder offlux-concentrating material 931, around which is wrapped a coil of wire932.

-   -   a. The cylinder may be long or short relative to the length of        the cell.

2. As shown in FIG. 11 b, a cell 930 may have a portion offlux-concentrating material 931 on its surface, around which is wrappeda coil of wire 932.

-   -   a. The portion may be conformed to the surface of the cell, or        embedded within it.    -   b. Its area may be large or small relative to the circumference        of the cell, and long or short relative to the length of the        cell.

3. As shown in FIG. 11 c, a cell 930 may contain a portion offlux-concentrating material 931 within it, around which is wrapped acoil of wire 932.

-   -   a. The portion may be substantially flat, cylindrical, rod-like,        or any other shape.    -   b. Its width may be large or small relative to the diameter of        the cell    -   c. Its length may be large or small relative to the length of        the cell

In any of these cases, the flux-concentrator may be a functional part ofthe battery enclosure (for example, an outer zinc electrode) or thebattery itself (for example, an inner electrode).

Issues relating to charging of secondary cells (e.g. AA rechargeablecells in-situ within an appliance include:

Terminal voltage could be higher than normal.

Cells in series may behave strangely, particularly in situations wheresome cells are charged, others not.

Having to provide enough power to run the device and charge the cell.

If fast-charging is effected incorrectly, the cells may be damaged.

Accordingly, some sophisticated charge-control means to meter inductivepower to the appliance and the cell is advantageously provided.Furthermore, it becomes more important for the primary unit to be ableto indicate a “charged” condition, since the secondary cell or batterymay not be easily visible when located inside an electrical device.

A cell or battery enabled in this fashion may be charged whilst fittedin another device, by placing the device onto the primary unit, orwhilst outside the device by placing the cell or battery directly ontothe primary unit.

Batteries enabled in this fashion may be arranged in packs of cells asin typical devices (e.g. end-to-end or side-by-side), allowing a singlepack to replace a set of cells.

Alternatively, the secondary device may consist of a flat “adapter”which fits over the batteries in a device, with thin electrodes whichforce down between the battery electrodes and the device contacts.

Rotating Electromagnetic Field

In the coils such as those in FIG. 6, 9 a and 9 b, the secondary deviceswill generally only couple effectively when the windings are placedsubstantially parallel to the direction of net current flow in theprimary conductor as shown by the arrow 1. In some applications, onemight require a primary unit which will transfer power effectively tosecondary devices regardless of their rotation as long as:

the central axis of the secondary conductor is not perpendicular to theplane and;

the secondary device is in close proximity to the primary unit

To enable this, it is possible to have two coils, for example onepositioned on top of the other or one woven into or otherwise associatedwith the other, the second coil capable of generating a net current flowsubstantially perpendicular to the direction of the first coil at anypoint in the active area of the primary unit. These two coils may bedriven alternately such that each is activated for a certain period oftime. Another possibility is to drive the two coils in quadrature suchthat a rotating magnetic dipole is generated in the plane. This isillustrated in FIG. 9. This is also possible with other combinations ofcoil configurations.

Resonant Circuits

It is known in the art to drive coils using parallel or series resonantcircuits. In series resonant circuits for example, the impedance of thecoil and the capacitor are equal and opposite at resonance, hence thetotal impedance of the circuit is minimised and a maximum current flowsthrough the primary coil. The secondary device is typically also tunedto the operating frequency to maximise the induced voltage or current.

In some systems like the electric toothbrush, it is common to have acircuit which is detuned when the secondary device is not present andtuned when the secondary device is in place. The magnetic materialpresent in the secondary device shifts the self-inductance of theprimary unit and brings the circuit into resonance. In other systemslike passive radio tags, there is no magnetic material in the secondarydevice and hence does not affect the resonant frequency of the system.These tags are also typically small and used far from the primary unitsuch that even if magnetic material is present, the inductance of theprimary is not significantly changed.

In the proposed system, this is not the case:

High permeability magnetic material may be present in the secondarydevice and is used in close proximity to the primary unit;

One or more secondary devices may be brought in close proximity to theprimary unit simultaneously.

This has the effect of shifting the inductance of the primarysignificantly and also to different levels depending on the number ofsecondary devices present on the pad. When the inductance of the primaryunit is shifted, the capacitance required for the circuit to resonant ata particular frequency also changes. There are three methods for keepingthe circuit at resonance:

By means of a control system to dynamically change the operatingfrequency;

By means of a control system to dynamically change the capacitance suchthat resonance is achieved at the predefined frequency;

By means of a low Q system where the system remains in resonance over arange of inductances.

The problem with changing the operating frequency is that the secondarydevices are typically configured to resonate at a predefined frequency.If the operating frequency changes, the secondary device would bedetuned. To overcome this problem, it is possible to change thecapacitance instead of the operating frequency. The secondary devicescan be designed such that each additional device placed in proximity tothe primary unit will shift the inductance to a quantised level suchthat an appropriate capacitor can be switched in to make the circuitresonate at a predetermined frequency. Because of this shift in resonantfrequency, the number of devices on the charging surface can be detectedand the primary unit can also sense when something is brought near ortaken away from the charging surface. If a magnetically permeable objectother than a valid secondary device is placed in the vicinity of thecharging surface, it is unlikely to shift the system to the predefinedquantised level. In such circumstances, the system could automaticallydetune and reduce the current flowing into the coil.

For a better understanding of the present invention and to show how itmay be carried into effect, reference shall now be made, by way ofexample only, to the accompanying drawings, in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the magnetic design of typical prior art contact-less powertransfer systems which require accurate alignment of the primary unitand secondary device;

FIG. 2 a shows the magnetic design of another typical prior artcontact-less power transfer system which involves a large coil in theprimary unit;

FIG. 2 b shows the non-uniform field distribution inside the large coilat 5 mm distance from the plane of the coil, exhibiting a minimum in thecentre;

FIG. 3 shows a multiple-coil system where each coil is independentlydriven such that a localised field can be generated.

FIG. 4 a shows an embodiment of the proposed system which demonstrates asubstantial departure from prior art with no secondary devices present;

FIG. 4 b shows an embodiment of the proposed system with two secondarydevices present;

FIG. 4 c shows a cross section of the active area of the primary unitand the contour lines of the magnetic flux density generated by theconductors.

FIG. 4 d shows the magnetic circuit for this particular embodiment ofthe proposed invention;

FIG. 5 shows a schematic drawing of an embodiment of the primary unitand the secondary device;

FIG. 6 a to 6 l show some alternative embodiment designs for the fieldgenerating means or a component of the field generating means of theprimary unit;

FIGS. 7 a and 7 b show some possible designs for the magnetic unit ofthe secondary device;

FIGS. 8 a-8 f show the effect of flux guides (the thickness of the fluxguide has been exaggerated for clarity);

FIG. 8 a shows that without flux guides, the field tends to fringe intothe air directly above the active area;

FIG. 8 b shows the direction of current flow in the conductors in thisparticular embodiment;

FIG. 8 c shows that the flux is contained within the flux guides whenmagnetic material is placed on top of the charging area;

FIG. 8 d shows a secondary device on top of the primary unit;

FIG. 8 e shows a cross section of the primary unit without any secondarydevices;

FIG. 8 f shows a cross section of the primary unit with a secondarydevice on top and demonstrates the effect of using a secondary core withhigher permeability than the flux guide.

FIG. 9 a shows a particular coil arrangement with a net instantaneouscurrent flow shown by the direction of the arrow;

FIG. 9 b shows a similar coil arrangement to FIG. 9 a except rotated by90 degrees;

FIG. 9 c shows the charging area of the primary unit if the coil of FIG.9 a is placed on top of FIG. 9 b. If the coil in FIG. 9 a is driven inquadrature to FIG. 9 b, the effect is a rotating magnetic dipole shownhere;

FIG. 10 shows the case where the secondary device has an axial degree ofrotation;

FIG. 11 shows various arrangements of secondary devices with axialdegrees of rotation;

FIG. 12 a and FIG. 12 b show another embodiment of the type of coilarrangement shown in FIG. 9 a and FIG. 9 b; and

FIG. 13 shows a simple embodiment of driving unit electronics.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring firstly to FIG. 1, there is shown two examples of prior artcontact-less power transfer systems which both require accuratealignment of a primary unit and a secondary device. This embodiment istypically used in electric toothbrush or mobile phone chargers.

FIG. 1 a shows a primary magnetic unit 100 and a secondary magnetic unit200. On the primary side, a coil 110 is wound around a magnetic core 120such as ferrite. Similarly, the secondary side consists of a coil 210wound around another magnetic core 220. In operation, an alternatingcurrent flows in to the primary coil 110 and generates lines of flux 1.When a secondary magnetic unit 200 is placed such that it is axiallyaligned with the primary magnetic unit 100, the flux 1 will couple fromthe primary into the secondary, inducing a voltage across the secondarycoil 210.

FIG. 1 b shows a split transformer. The primary magnetic unit 300consists of a U-shaped core 320 with a coil 310 wound around it. Whenalternating current flows into the primary coil 310, changing lines offlux are generated 1. The secondary magnetic unit 400 consists of asecond U-shaped core 420 with another coil 410 wound around it. When thesecondary magnetic unit 400 is placed on the primary magnetic unit 300such that the arms of the two U-shaped cores are in alignment, the fluxwill couple effectively into the core of the secondary 420 and inducevoltage across the secondary coil 410.

FIG. 2 a is another embodiment of prior art inductive systems typicallyused in powering radio frequency passive tags. The primary typicallyconsists of a coil 510 covering a large area. Multiple secondary devices520 will have voltage induced therein when they are within the areaencircled by the primary coil 510. This system does not require thesecondary coil 520 to be accurately aligned with the primary coil 510.FIG. 2 b shows a graph of the magnitude of magnetic flux intensityacross the area encircled by the primary coil 510 at 5 mm above theplane of the primary coil. It shows a non-uniform field, which exhibitsa minimum 530 at the centre of the primary coil 510.

FIG. 3 is another embodiment of a prior art inductive system wherein amultiple coil array is used. The primary magnetic unit 600 consists ofan array of coils including coils 611, 612, 613. The secondary magneticunit 700 may consist of a coil 710. When the secondary magnetic unit 700is in proximity to some coils in the primary magnetic unit 600, thecoils 611, 612 are activated while other coils such as 613 remaininactive. The activated coils 611, 612 generate flux, some of which willcouple into the secondary magnetic unit 700.

FIG. 4 shows an embodiment of the proposed invention. FIG. 4 a shows aprimary coil 710 wound or printed in such a fashion that there is a netinstantaneous current flow within the active area 740. For example, if adc current flows through the primary coil 710, the conductors in theactive area 740 would all have current flowing in the same direction.Current flowing through the primary coil 710 generates flux 1. A layerof magnetic material 730 is present beneath the charging area to providea return path for the flux. FIG. 4 b shows the same primary magneticunit as shown in FIG. 4 a with two secondary devices 800 present. Whenthe secondary devices 800 are placed in the correct orientation on topof the charging area 740 of the primary magnetic unit, the flux 1 willflow through the magnetic core of the secondary devices 800 instead offlowing through the air. The flux 1 flowing through the secondary corewould hence induce current in the secondary coil.

FIG. 4 c shows some contour lines for the flux density of the magneticfield generated by the conductors 711 in the charging area 740 of theprimary magnetic unit. There is a layer of magnetic material 730 beneaththe conductors to provide a low reluctance return path for the flux.

FIG. 4 d shows a cross-section of the charging area 740 of the primarymagnetic unit. A possible path for the magnetic circuit is shown. Themagnetic material 730 provides a low reluctance path for the circuit andalso the magnetic core 820 of the secondary magnetic device 800 alsoprovides a low reluctance path. This minimizes the distance the flux hasto travel through the air and hence minimizes leakage.

FIG. 5 shows a schematic drawing of an embodiment of the whole system ofthe proposed invention. In this embodiment, the primary unit consists ofa power supply 760, a control unit 770, a sensing unit 780 and anelectromagnetic unit 700. The power supply 760 converts the mains (orother sources of power) into a dc supply at an appropriate voltage forthe system. The control unit 770 controls the driving unit 790 whichdrives the magnetic unit 700. In this embodiment, the magnetic unitconsists of two independently driven components, coil 1 and coil 2,arranged such that the conductors in the charging area of coil 1 wouldbe perpendicular to the conductors in the charging area of coil 2. Whenthe primary unit is activated, the control unit causes a 90-degree phaseshift between the alternating current that flows through coil 1 and coil2. This creates a rotating magnetic dipole on the surface of the primarymagnetic unit 700 such that a secondary device is able to receive powerregardless of its rotational orientation (See FIG. 9). In standby modewhere no secondary devices are present, the primary unit is detuned andcurrent flow into the magnetic unit 700 is minimised. When a secondarydevice is placed on top of the charging area of the primary unit, theinductance of the primary magnetic unit 700 is changed. This brings theprimary circuit into resonance and the current flow is maximised. Whenthere are two secondary devices present on the primary unit, theinductance is changed to yet another level and the primary circuit isagain detuned. At this point, the control unit 770 uses feedback fromthe sensing unit 780 to switch another capacitor into the circuit suchthat it is tuned again and current flow is maximised. In thisembodiment, the secondary devices are of a standard size and a maximumof six standard-sized devices can receive power from the primary unitsimultaneously. Due to the standard sizes of the secondary devices, thechange in inductance due to the change in secondary devices in proximityis quantized to a number of predefined levels such that only a maximumof 6 capacitances is required to keep the system operating at resonance.

FIGS. 6 a to 6 l show a number of different embodiments for the coilcomponent of the primary magnetic unit. These embodiments may beimplemented as the only coil component of the primary magnetic unit, inwhich case the rotation of the secondary device is important to thepower transfer. These embodiments may also be implemented incombination, not excluding embodiments which are not illustrated here.For example, two coils illustrated in FIG. 6 a may be placed at 90degrees to each other to form a single magnetic unit. In FIGS. 6 a to 6e, the charging area 740 consists of a series of conductors with netcurrent generally flowing in the same direction. In certainconfigurations, such as FIG. 6 c, there is no substantial linkage whenthe secondary device is placed directly over the centre of the coil andhence power is not transferred. In FIG. 6 d, there is no substantiallinkage when the secondary device is positioned in the gap between thetwo charging areas 740.

FIG. 6 f shows a specific coil configuration for the primary unitadapted to generate electromagnetic field lines substantially parallelto a surface of the primary unit within the charging area 740. Twoprimary windings 710, one on either side of the charging area 740, areformed about opposing arms of a generally rectangular flux guide 750made out of a magnetic material, the primary windings 710 generatingopposing electromagnetic fields. The flux guide 750 contains theelectromagnetic fields and creates a magnetic dipole across the chargingarea 740 in the direction of the arrows indicated on the Figure. When asecondary device is placed in the charging area 740 in a predeterminedorientation, a low reluctance path is created and flux flows through thesecondary device, causing effective coupling and power transfer. It isto be appreciated that the flux guide 750 need not be continuous, andmay in fact be formed as two opposed and non-linked horseshoecomponents.

FIG. 6 g shows another possible coil configuration for the primary unit,the coil configuration being adapted to generate electromagnetic fieldlines substantially parallel to the charging surface of the primary unitwithin the charging area 740. A primary winding 710 is wound around amagnetic core 750 which may be ferrite or some other suitable material.The charging area 740 includes a series of conductors with instantaneousnet current generally flowing in the same direction. The coilconfiguration of FIG. 6 g is in fact capable of supporting or defining acharging area 740 on both upper and lower faces as shown in the drawing,and depending on the design of the primary unit, one or both of thecharging areas may be made available to secondary devices.

FIG. 6 h shows a variation of the configuration of FIG. 6 g. Instead ofthe primary windings 710 being evenly spaced as in FIG. 6 g, thewindings 710 are not evenly spaced. The spacing and variations thereincan be selected or designed so as to provide improved uniformity ofperformance or field strength levels over the charging area 740.

FIG. 6 i shows an embodiment in which two primary windings 710 as shownin FIG. 6 g are located in a mutually orthogonal configuration so as toenable a direction of the field lines to be dynamically switched orrotated to other orientations about the plane of the charging surface.

FIGS. 6 j and 6 k show additional two-coil configurations for theprimary unit which are not simple geometric shapes with substantiallyparallel conductors.

In FIG. 6 j, line 710 indicates one of a set of current-carryingconductors lying in the plane of the charging surface 600. The shape ofthe main conductor 710 is arbitrary and need not be a regular geometricfigure—indeed, conductor 710 may have straight and curved sections andmay intersect with itself. One or more subsidiary conductors 719 arearranged alongside and generally parallel (at any given local point) tothe main conductor 710 (only two subsidiary conductors 719 are shownhere for clarity). Current flow in subsidiary conductors 719 will be inthe same direction as in the main conductor 710. The subsidiaryconductors 719 may be connected in series or parallel so as to form asingle coil arrangement.

In FIG. 6 k, a set of current-carrying conductors 720 (only some ofwhich are shown for clarity) is arranged in the plane of the chargingsurface 600. A main conductor 710 is provided as in FIG. 6 j, and theconductors 720 are each arranged so as to be locally orthogonal to themain conductor 710. The conductors 720 may be connected in series orparallel so as to form a single coil arrangement. If a first sinusoidalcurrent is fed into the conductor 710, and a second sinusoidal currenthaving a 90° phase shift relative to the first current is fed into thecoil 720, then by varying the relative proportions and signs of the twocurrents a direction of a resultant electromagnetic field vector at mostpoints on the charging area 740 will be seen to rotate through 360°.

FIG. 61 shows yet another alternative arrangement in which the magneticcore 750 is in the shape of a round disc with a hole in the centre. Thefirst set of current carrying conductors 710 is arranged in a spiralshape on the surface of the round disc. The second set of conductors 720is wound in a toroidal format through the centre of the disc and out tothe perimeter in a radial fashion. These conductors can be driven insuch a way, for example with sinusoidal currents at quadrature, thatwhen a secondary device is placed at any point inside the charging area740 and rotated about an axis perpendicular to the charging area, nonulls are observed by the secondary device.

FIGS. 7 a and 7 b are embodiments of the proposed secondary devices. Awinding 810 is wound around a magnetic core 820. Two of these may becombined in a single secondary device, at right angles for example, suchthat the secondary device is able to effectively couple with the primaryunit at all rotations. These may also be combined with standard coils,as the ones shown in FIG. 2 a 520 to eliminate dead spots.

FIGS. 8 a-8 f show the effect of flux guides 750 positioned on top ofthe charging area. The thickness of the material has been exaggeratedfor the sake of clarity but in reality would be in the order ofmillimetres thick. The flux guides 750 will minimize leakage and containthe flux at the expense of reducing the amount of flux coupled to thesecondary device. In FIG. 8 a, a primary magnetic unit is shown withoutflux guides 750. The field will tend to fringe into the air directlyabove the charging area. With flux guides 750, as shown in FIG. 8 b to 8f, the flux is contained within the plane of the material and leakage isminimised. In FIG. 8 e, when there is no secondary device 800 on top,the flux remains in the flux guide 750. In FIG. 8 f, when a secondarydevice 800 is present with a relatively more permeable material as thecore, part of the flux will flow via the secondary device. Thepermeability of the flux guide 750 can be chosen such that it is higherthan that of typical metals such as steel. When other materials such assteel, which are not part of secondary devices 800, are placed on top,most of the flux will remain in the flux guide 750 instead of travellingthrough the object. The flux guide 750 may not be a continuous layer ofmagnetic material but may have small air gaps in them to encourage moreflux flow into the secondary device 800 when it is present.

FIG. 9 shows an embodiment of a primary unit whereby more than one coilis used. FIG. 9 a shows a coil 710 with a charging area 740 with currentflow parallel to the direction of the arrow 2. FIG. 9 b shows a similarcoil arranged at 90 degrees to the one in FIG. 9 a. When these two coilsare placed on top of each other such that the charging area 740overlaps, the charging area will look like the illustration in FIG. 9 c.Such an embodiment would allow the secondary device to be at anyrotation on top of the primary unit and couple effectively.

FIG. 10 shows an embodiment where the secondary device has an axialdegree of rotation, for example where it is, or is embedded within, abattery cell. In this embodiment the secondary device may be constructedsuch that it couples to the primary flux when in any axial rotation (rA)relative to the primary unit (910), as well as having the same degreesof freedom described above (i.e. translational (X,Y) and optionallyrotational perpendicular to the plane of the primary (rZ)).

FIG. 11 a shows one arrangement where a rechargeable battery cell 930 iswrapped with an optional cylinder of flux-concentrating material 931which is itself wound with copper wire 932. The cylinder may be long orshort relative to the length of the cell.

FIG. 11 b shows another arrangement where the flux-concentratingmaterial 931 covers only part of the surface of the cell 930, and hascopper wire 932 wrapped around it (but not the cell). The material andwire may be conformed to the surface of the cell. Their area may belarge or small relative to the circumference of the cell, and long orshort relative to the length of the cell.

FIG. 11 c shows another arrangement where the flux-concentratingmaterial 931 is embedded within the cell 930 and has copper wire 932wrapped around it. The material may be substantially flat, cylindrical,rod-like, or any other shape, its width may be large or small relativeto the diameter of the cell, and its length may be large or smallrelative to the length of the cell.

In any case shown in FIGS. 10 and 11, any flux-concentrating materialmay also be a functional part of the battery enclosure (for example, anouter zinc electrode) or the battery itself (for example, an innerelectrode).

In any case shown in FIGS. 10 and 11, the power may be stored in asmaller standard cell (e.g. AAA size) fitted within the larger standardcell enclosure (e.g. AA).

FIG. 12 shows an embodiment of a primary unit similar to that shown inFIG. 9. FIG. 12 a shows a coil generating a field in a directionhorizontal to the page, FIG. 12 b shows another coil generating a fieldvertical to the page, and the two coils would be mounted in asubstantially coplanar fashion, possibly with one above the other, oreven intertwined in some fashion. The wire connections to each coil areshown 940 and the charging area is represented by the arrows 941.

FIG. 13 shows a simple embodiment of the Driving Unit (790 of FIG. 5).In this embodiment there is no Control Unit. The PIC processor 960generates two 23.8 kHz square waves 90 degrees out of phase with oneanother. These are amplified by components 961 and driven into two coilcomponents 962, which are the same magnetic units shown in FIG. 12 a andFIG. 12 b. Although the driving unit is providing square waves, the highresonant “Q” of the magnetic units shapes this into a sinusoidalwaveform.

The preferred features of the invention are applicable to all aspects ofthe invention and may be used in any possible combination.

Throughout the description and claims of this specification, the words“comprise” and “contain” and variations of the words, for example“comprising” and “comprises”, mean “including but not limited to”, andare not intended to (and do not) exclude other components, integers,moieties, additives or steps.

1. A portable electrical or electronic device, adapted to receive powerinductively from an external unit that has a field generating surfaceand a field generator which generates an electromagnetic field at orover the field generating surface, the device being adapted to receivepower from the external unit when placed in an intended power-receivingdisposition on or in proximity to said field generating surface andbeing separable from the external unit when not receiving powertherefrom, the device comprising: a housing including a predeterminedportion having an external surface which faces said field generatingsurface when the device is placed in said power-receiving disposition,said predetermined portion also having an internal surface; and amagnetic core component arranged within said housing on or in proximityto said internal surface of said predetermined portion so that the corecomponent couples with said field when the device is in its saidpower-receiving disposition, the magnetic core component including athin sheet of magnetic material and also including a coil wound aroundsaid sheet for receiving power inductively from the external unit, thesheet and the coil being arranged so that a longitudinal axis of saidsheet and a central axis of said coil each extend generally parallel tosaid field generating surface when the device is in said power-receivingdisposition.
 2. A portable electrical or electronic device as claimed inclaim 1, wherein said thin sheet is substantially flat.
 3. A portableelectrical or electronic device as claimed in claim 1, wherein said thinsheet is curved.
 4. A portable electrical or electronic device asclaimed in claim 1, wherein said coil extends in its axial directionover a distance that is large compared to a thickness of said magneticcore component.
 5. A portable electrical or electronic device as claimedin claim 1, wherein the largest dimension of said thin sheet is in thedirection of said central axis of said coil.
 6. A portable electrical orelectronic device as claimed in claim 1, wherein said magnetic materialis amorphous magnetically permeable material.
 7. A portable electricalor electronic device as claimed in claim 1, wherein said magnetic corecomponent has two such coils, the respective central axes of said twocoils extending in mutually orthogonal directions generally parallel tosaid field generating surface when the device is in said power-receivingdisposition.
 8. A rechargeable battery adapted to receive powerinductively from an external unit when fitted into a battery holder in aportable electrical or electronic device, the external unit having afield generating surface and a field generator which generates anelectromagnetic field at or over the field generating surface, and thedevice being adapted to be placed in an intended power-receivingdisposition on or in proximity to said field generating surface of theexternal unit when the battery is to be recharged, and the devicecomprising a housing including a predetermined portion having anexternal surface which faces said field generating surface when saiddevice is placed in its said power-receiving disposition, the batterycomprising: a magnetic core component carried in or by said battery insuch a way that when the battery is retained by said battery holder andsaid device is in its said power-receiving disposition the corecomponent is in proximity to said internal surface of said predeterminedportion and couples with the field, the magnetic core componentincluding a thin sheet of magnetic material and also including a coilwound around said sheet for receiving power inductively from theexternal unit, the sheet and the coil being arranged so that alongitudinal axis of the sheet and a central axis of the coil eachextend generally parallel to said field generating surface when thebattery is retained in said battery holder and the device is in its saidpower-receiving disposition.
 9. A rechargeable battery as claimed inclaim 8, wherein said thin sheet is substantially flat.
 10. Arechargeable battery as claimed in claim 8, wherein said thin sheet iscurved.
 11. A rechargeable battery as claimed in claim 8, wherein saidcoil extends in its axial direction over a distance that is largecompared to a thickness of said magnetic core component.
 12. Arechargeable battery as claimed in claim 8, wherein said magneticmaterial is amorphous magnetically permeable material.
 13. Arechargeable battery as claimed in claim 8, wherein: the battery holderis adapted to retain the battery in the device with its longitudinalaxis extending generally parallel to said field generating surface whenthe device is in its said power-receiving disposition; and the sheet andthe coil are arranged so that said longitudinal axis of the sheet andsaid central axis each extend generally parallel to said fieldgenerating surface when the battery is so retained in said batteryholder and the device is in its said power-receiving disposition.
 14. Arechargeable battery as claimed in claim 8, wherein the magnetic corecomponent is at least partially wrapped around an axis of the batterysuch that it couples with an electromagnetic field generated by saidexternal unit in any rotation about the axis when the device is in itssaid power-receiving disposition and the battery is retained in saidbattery holder.
 15. A rechargeable battery adapted to receive powerinductively from a primary unit when fitted into a space in a portableelectrical or electronic device, the device comprising a cover elementhaving a substantially planar portion with inner and outer surfaces andbeing adapted to be placed with said outer surface on or in proximity tosuch a primary unit when the battery is to be recharged, and the devicebeing adapted to retain the battery in the space with its longitudinalaxis extending generally parallel to a plane of said planar portion, thebattery comprising: a power-receiving element comprising a coil which isin close proximity to said inner surface of said cover element when thecell is so retained in said space and which has a central axis thatextends generally parallel to a plane of said planar portion, forreceiving power inductively from the primary unit when the device is soplaced on or in proximity to the primary unit; and a rechargeableenergy-storing element connected to the power-receiving element forstoring the power received inductively by the power-receiving element;wherein said power-receiving element is in the form of a thin sheet. 16.A rechargeable battery as claimed in claim 15, wherein said thin sheetis substantially flat.
 17. A rechargeable battery as claimed in claim15, wherein said thin sheet is curved.
 18. A rechargeable battery asclaimed in claim 15, wherein said power-receiving element furthercomprises a core of magnetic material, said core having a longitudinalaxis which extends generally parallel to said plane.
 19. A rechargeablebattery as claimed in claim 18, wherein said coil is wound about saidcore.
 20. A rechargeable battery as claimed in claim 18, wherein saidcoil extends in its axial direction over a distance that is largecompared to a thickness of said power-receiving element.
 21. Arechargeable battery as claimed in claim 18, wherein said core is madeof amorphous magnetically permeable material.
 22. A rechargeable batteryas claimed in claim 15, wherein said power-receiving element has twosuch coils, the respective central axes of said two coils extending inmutually orthogonal directions generally parallel to said plane.
 23. Arechargeable battery as claimed in claim 15, wherein said portableelectrical or electronic device has a metal plane extending generallyparallel to said plane of said planar portion of said cover element. 24.A rechargeable battery as claimed in claim 15, wherein the portableelectrical or electronic device has a printed circuit board extendinggenerally parallel to a plane of said planar portion of said coverelement.
 25. A rechargeable battery as claimed in claim 15, wherein saidplanar portion of said cover element includes metal.
 26. A rechargeablebattery as claimed in claim 18, wherein, when the battery is retained insaid space, said core is located between said cover element andcomponents of the device susceptible to electromagnetic fields so thatthe core can serve to reduce the effects on such components of anelectromagnetic field generated by the primary unit.
 27. A rechargeablebattery as claimed in claim 15, wherein said rechargeable batteryfurther comprises a power conversion unit which converts power receivedinductively by the power-receiving element into a form suitable fordelivery to outside said battery through external electrical connectionsthereof, or into a form suitable for recharging the energy-storingelement, or into both said forms.
 28. A rechargeable battery as claimedin claim 27, wherein said rechargeable battery has a charge-control unitoperable, when the power-receiving element is receiving powerinductively, to meter the supply of inductively-received power to theexternal electrical connections and to the energy-storing element.
 29. Arechargeable battery as claimed in claim 15, having an enclosure andexternal electrical connections similar in dimensions to anindustry-standard battery.
 30. A rechargeable battery adapted to receivepower inductively from a primary unit when fitted into a space in aportable electrical or electronic device, the device comprising a coverelement having a substantially planar portion with inner and outersurfaces and being adapted to be placed with said outer surface on or inproximity to such a primary unit when the battery is to be recharged,and the device being adapted to retain the battery in the space with itslongitudinal axis extending generally parallel to a plane of said planarportion, the battery comprising: a power-receiving element comprising acoil which is in close proximity to said inner surface of said coverelement when the cell is so retained in said space and which has acentral axis that extends generally parallel to a plane of said planarportion, for receiving power inductively from the primary unit when thedevice is so placed on or in proximity to the primary unit; and arechargeable energy-storing element connected to the power-receivingelement for storing the power received inductively by thepower-receiving element; wherein a thickness of said power-receivingelement, measured in a direction perpendicular to said plane, is smallrelative to the dimensions of the power-receiving element parallel tosaid plane.
 31. A rechargeable battery adapted to receive powerinductively from a primary unit, the battery comprising: a generallycylindrical body having a central axis; a power-receiving element,comprising a coil having a central axis extending generally in parallelwith said central axis of said body, for receiving power inductivelyfrom the primary unit when the battery is placed on or in proximity to apower transfer surface of the primary unit with said central axis ofsaid body lying across the surface; and a rechargeable energy-storingelement connected to said power-receiving element for storing the powerreceived inductively by the power-receiving element; wherein saidpower-receiving element is in the form of a thin sheet.
 32. Arechargeable battery as claimed in claim 31, wherein said thin sheet iscurved.
 33. A rechargeable battery as claimed in claim 31, wherein saidthin sheet is wrapped circumferentially around said body or aroundanother generally cylindrical component of the battery.
 34. Arechargeable battery as claimed in claim 31, wherein saidpower-receiving element further comprises a core of magnetic material,said core having a longitudinal axis which extends generally parallel tosaid central axis of said body.
 35. A rechargeable battery as claimed inclaim 34, wherein said coil is wound about said core.
 36. A rechargeablebattery as claimed in claim 34, wherein said coil extends in its axialdirection over a distance that is large compared to a thickness of saidpower-receiving element.
 37. A rechargeable battery as claimed in claim34, wherein said core is made of amorphous magnetically permeablematerial.
 38. A rechargeable battery as claimed in claim 31, whereinsaid rechargeable battery further comprises a power conversion unitwhich converts power received inductively by the power-receiving elementinto a form suitable for delivery to outside said battery throughexternal electrical connections thereof, or into a form suitable forrecharging the energy-storing element, or into both said forms.
 39. Arechargeable battery as claimed in claim 30, wherein said rechargeablebattery has a charge-control unit operable, when the power-receivingelement is receiving power inductively, to meter the supply ofinductively-received power to the external electrical connections and tothe energy-storing element.
 40. A rechargeable battery as claimed inclaim 31, having an enclosure and external electrical connectionssimilar in dimensions to an industry-standard battery.